NTC thermistor in series in the ac circuit mainly ACTS as "current protection in order to avoid the" electronic circuit in the boot of the instant surge current in the power supply circuit through a power type NTC thermistor, can effectively inhibit the surge current when the phone is switched on, and after finish the inhibitory effect of surge current, due to continued through its current role, Power type NTC thermistor resistance will fall to the very small extent, its power consumption is negligible, will not affect the normal working current, therefore, used in the power supply circuit of power type NTC thermistor, suppress surge when the phone is switched on, to ensure that the electronic equipment from damage of the most simple and effective measures.
Varistor is a Chinese term which means "the positive value varies with voltage over a certain range of current and voltage", or "the value of the resistance is sensitive to voltage". The corresponding English name is "Voltage Dependent Resistor" or VDR. The resistor material of varistor is semiconductor, so it is a kind of semiconductor resistor. Now a large number of "zinc oxide" (Zn0) varistors, its main material is a divalent element (Zn) and hexavalent element oxygen (O) composition. So from the material point of view, zinc oxide varistor is a "ⅱ - ⅵ I oxide semiconductor". In Taiwan, China, the varistor is named after its purpose, called "surge absorber". Varistors are sometimes called "surge suppressors (absorbers)" for their use.
Varistor belongs to the "safety valve" in the circuit, the greatest characteristic of varistor is when to add on it when the voltage is lower than its threshold "UN", current flow through the tiny, equivalent to a completely closed valve, when the voltage is more than "UN", through its current is added, is equivalent to the valve open state, through the implementation of this feature, Can suppress the circuit often abnormal overvoltage, protect the circuit from overvoltage damage.
